The present invention is concerned with an information display system capable of presenting video pictures and other forms of information on a display screen constituted by a number of lamp matrix modules.
In many present-day sports and entertainment facilities, large display screens are installed at elevated positions where they may be conveniently viewed by the audience. These screens serve not only to present standard sports scoreboard data, but also to provide instant replays, as well as slow motion and close-ups. These large display screens have also found a variety of other uses and applications including, for example, giant video games, views of patrons on a disco dance floor, music activated video effects, and so on.
Television projection systems have been used in the prior art to provide the large screen displays referred to above. However, the projection television information display system is unsuitable under daylight, or under outdoor lighting conditions where the ambient light level is high. To meet the requirements of a high intensity outdoor display screen viewable by a large audience, lamp matrices have been developed which are formed by a large array of standard incandescent lamps, the lamps being selectively controlled to display alpha-numeric information and/or to produce pictorial video images whose picture elements are defined by the incandescent lamps of the array.
One commercially available incandescent lamp matrix display system is manufactured and sold under the trademark "Telescreen" by the Conrac Corporation. Similar systems are also manufactured and sold by the Stewart-Warner Company. These display systems, in each instance, include an array of incandescent lamps, each of which produces light of a controllable intensity, and each of which is capable of reproducing the gray shade scale of black and white broadcast television. The Stewart-Warner systems are described, for example, in U.S. Pat. Nos. 3,941,926 and 4,009,335. Similar systems are described in U.S. Pat. Nos. 4,194,215 and 4,134,132.
U.S. Pat. No. 4,063,234--Arn et al, for example, illustrates and describes a flat screen video display apparatus in which a plurality of addressale incandescent lamps are arranged in an X-Y matrix. The gray scale visual effect of the video information presented by the display is achieved by controlling the length of time of illumination of each of the lamps in the display. Each lamp is connected in series with a source of power and a switchable solid state device, such as an SCR or a transistor. The lamps are normally turned off. However, in the presence of a video signal above a predetermined threshold, the lamps are selectively turned on. Pulse width modulation is provided to control the gray scale visual effect of each lamp after it has been turned on.
An objective of the present invention is to provide a video matrix display system of the general type described above, but one which is modular in nature, and which utilizes an expandable array of incandescent lamps to provide a low cost version of the prior art displays. The modular display of the present invention may be used to provide the small size 10'.times.15' conventional display using 9,600 lamps; or the larger size 15'.times.20' conventional display using 19,200 lamps; or any other desired size merely by selecting the number of modules to be included in the display. The lamps used in the preferred embodiment are small, long life indicator types of from 1/2-12 watt power. Each module may contain, for example, 400 lamps each, to allow for a variety of display formats and ease of servicing.
A video digitizer unit is included in the matrix display system of the invention, and this digitizer serves to convert any standard video signal into digital signals which selectively control the brightness of the incandescent lamps of the array. Since the video and control signals are digital, no adjustments are required for the display itself. The system to be described uses efficient switching techniques so that even with 1/2 watt lamps, over 80% of the power is delivered to the lamps, minimizing cooling problems. The matrix display system to be described consists of a power supply, a video digitizer unit, and a modular display unit consisting, for example, of up to 48 modules, constructed to require a minimum of interconnections.
The main power supply is a simple 30-volt unregulated, three-phase rectifier type which requires no filter capacitors for maximum reliability. A secondary low current 10-volt supply is also included in addition to the 30-volt main supply. For a display using 900 milliwatt lamps, an average of 5 amps per module are required, or 240 amps for 48 modules. With such lamps, the three-phase power required is 208 volts at slightly over 15 amps. The power supply may be remotely switched on from the video digitizer unit.
Each module in the matrix display system to be described includes electronics incorporating appropriate drive circuitry, and a memory for its 400 lamps, which are arranged in twenty rows of twenty lamps each. In this way, and by using a multiplexed X-Y assembly, each drive transistor in the drive circuitry controls twenty lamps. The modules for the standard indoor system are, for example, 30".times.30".times.4", and weigh 19 pounds. The electronics consists of a driver board with all the switching and digital circuits mounted on that board; the driver boards with driver transistors; and two lamp boards with each lamp board being equipped with sockets for 200 lamps and mounting hardware. Replacement of a lamp, or lamp board, or complete module, is made simple for minimum downtime. There are only three power connections and a connector for the two digital signals required for each module.
It is to be understood, of course, that the foregoing specific numbers are for explanation purposes only, and are not intended to limit the invention in any way.
The video digitizer unit selects from three standard video signals, one to sample and digitize the signal to a sixty-four level code for transmission in real time to the lamp matrix of each module, together with a signal to adjust the brightness levels of the lamps for a proper approximation to the video gray scale. A dark level and white level adjustment is included to set the sixty-four levels of brightness to match the range of shades in the incoming video signal. A "freeze" mode is also provided, in which some of the video signals are stopped, allowing memories in the display to hold the image still.
The matrix display itself is formed as an array of the modules, arranged in an X-Y matrix, to provide economy of interconnections and parts included in the design of each module. The total number of signals required to drive the matrix is a function of its linear size, but not its area, so that even for a large number of lamps, the number of required signals is small. For example, the number of signals required to drive a single module is two; for twenty-four modules in a 10'.times.15' module display, the number of drive signals required is seven; for a forty-eight module system in a 15'.times.20' display, the required number of drive signals is nine to control 19,200 lamps. Regardless of displayize, there are only three power connections.